Touch panel and method of manufacturing the same

ABSTRACT

Upper substrate  1  that has upper conductive layer  2  formed on a bottom surface thereof is bonded to lower substrate  3  that has lower conductive layer  4  opposed to upper conductive layer  2  with a predetermined space held therebetween on a top surface of lower substrate  3  by adhesive layer  15  that is made of a thermoplastic resin containing a tackifier dispersed therein and bonding property of the adhesive layer is enhanced by pressing. Addition of the tackifier increases flexibility of adhesive layer  15  and performs bonding with a large adhesive area at pressing. Thus, the width of adhesive layer  15  can be as small as approximately 1 to 1.5 mm. This can provide a smaller touch panel ensuring a predetermined touch sensitive area.

FIELD OF THE INVENTION

[0001] The present invention relates to a touch panel used for inputoperation in various kinds of electronic equipment and a method ofmanufacturing the touch panel.

BACKGROUND OF THE INVENTION

[0002] As electronic equipment has had more advanced and diversifiedfunctions in recent years, an increasing number of such equipment has anoptically transparent touch panel attached in front of liquid crystaldisplay elements so that characters, marks, and icons displayed on thedisplay elements are recognized and selected through the touch panel,and individual functions of the equipment are switched by depressing thetouch panel with a finger, or a touch screen pen.

[0003] Such a conventional touch panel is described with reference toFIG. 2. To facilitate understanding of a structure thereof, thedimension in the direction of the thickness is enlarged in the drawing.

[0004] As shown in FIG. 2, a conventional touch panel has opticallytransparent upper substrate 1 made of polyethylene terephthalate film orpolycarbonate film. On the bottom surface of the upper substrate,optically transparent upper conductive layer 2 made of indium tin oxideor tin oxide is formed by vacuum sputtering or other methods.

[0005] On the top surface of optically transparent lower substrate 3made of polyethylene terephthalate resin, glass or acrylic resin,optically transparent lower conductive layer 4 is formed. On the topsurface of lower conductive layer 4, a plurality of dot spacers 5 madeof epoxy resin or silicon resin, are formed to hold a predeterminedspace between upper conductive layer 2 and lower conductive layer 4.

[0006] Moreover, at both ends of upper conductive layer 2, a pair ofupper electrodes 6 is formed. On the other hand, at both ends of lowerconductive layer 4, a pair of lower electrodes 7 is formed. The pair ofupper electrodes 6 and the pair of lower electrode layers 7 areorthogonal to each other. In the description of FIG. 2, by routingeither upper electrode 6 or lower electrode 7, both electrodes areconfigured to oppose to each other at the same end. Each of upperelectrode 6 and lower electrode 7 is formed by printing paste made ofsilver, carbon, or other materials. These electrodes are covered withupper insulating layer 8 or lower insulating layer 9 made of polyesterresin.

[0007] Further, outer peripheries of these upper substrate 1 and lowersubstrate 3 are bonded by a frame-shaped spacer 10 so that upperconductive layer 2 and lower conductive layer 4 are opposed to eachother with a predetermined space held therebetween. Thus, the touchpanel is structured. Frame-shaped spacer 10 is structured so thatadhesive layers 10B are applied to the top and bottom surfaces of base10A made of polyethylene terephthalate film.

[0008] In a thus structured touch panel, upper lead electrodes 6 andlower lead electrodes 7 are connected to a detecting circuit (not shown)of electronic equipment. Depressing a touch sensitive area in whichdepressing operation and position-detecting operation are possible witha finger, pen flexes upper substrate 1 and brings upper conductive layer2 in the depressed position into contact with lower conductive layer 4.Voltages are sequentially applied to upper electrodes 6 and lowerelectrodes 7 by the detecting circuit. The detecting circuit detects thedepressed position according to resistance ratio of these pairs of upperelectrodes 6 and lower electrodes 7.

[0009] Incidentally, the touch sensitive area does not include spacer 10formed on the top surface of upper substrate 1. Spacer 10 is structuredso that adhesive layers 10B are applied to the top and bottom surfacesof base 10A as described above. Thus, even when a width of the spacer issmall to a curtain degree, a predetermined adhesive strength can beobtained. However, when a width of the spacer is extremely small,cutting or bonding operation is difficult. For this reason, the width isgenerally set to approximately 2.5 mm.

[0010] When adhesive layer 10B is directly printed on one of uppersubstrate 1 and lower substrate 3 without using spacer 10, the width ofthe adhesive layer can be made smaller. However, to obtain apredetermined adhesive strength, a width of not less than 2.5 mm isnecessary. Moreover, because upper substrate 1 and lower substrate 3must be bonded by hot press, heat at pressing may cause warps orundulations of upper substrate 1 or lower substrate 3.

[0011] In either case, a thermoplastic resin having adhesive propertieseven at room temperature is used in adhesive layer 10B. Thus, apredetermined width of the adhesive layer can provide a predeterminedadhesive strength at room temperature. However, when the touch panel isused under high temperatures and high humidity, the adhesive strength issmaller than that at room temperature, and thus so-called holdingstrength deteriorates. For this reason, actually, the adhesive layermust have a width exceeding 2.5 mm.

[0012] The conventional touch panel described above requires adhesivelayer 10B having a width exceeding 2.5 mm to ensure a predeterminedadhesive strength between upper substrate 1 and lower substrate 3 foruse under high temperatures and high humidity. For this reason, theconventional touch panel has the following problem. Because the wideradhesive layer reduces a touch sensitive area in which depressingoperation and position-detecting operation are possible, and because theoutside dimension measures a predetermined touch sensitive area plus awidth of spacer 10, the entire touch panel becomes large.

SUMMARY OF THE INVENTION

[0013] A touch panel of the present invention is structured so that anupper substrate that has an upper conductive layer formed on a bottomsurface thereof is bonded to a lower substrate that has a lowerconductive layer opposed to the upper conductive layer with apredetermined space held therebetween by an adhesive layer. The adhesivelayer is made of an adhesive material that contains a thermoplasticresin containing tackifier dispersed therein, and bonding property ofthe adhesive material is enhanced by pressing. Addition of the tackifierincreases flexibility of the adhesive layer and performs bonding with anadhesive area substantially increased at pressing. Thus, the width ofthe adhesive layer can be as small as approximately 1 to 1.5 mm. Thiscan provide a smaller touch panel ensuring a predetermined touchsensitive area.

[0014] A method of manufacturing a touch panel of the present inventionhas the step of bonding the touch panel using the adhesive material bypressing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a sectional view of a touch panel in accordance with anexemplary embodiment of the present invention.

[0016]FIG. 2 is a sectional view of a conventional touch panel.

DETAILED DESCRIPTION OF THE INVENTION

[0017] An exemplary embodiment of the present invention is describedhereinafter with reference to FIG. 1. In the description, same elementsused in the prior art are denoted with the same reference numbers andthe detailed description of those elements are omitted. To facilitateunderstanding of a structure thereof, the dimension in the direction ofthe thickness is enlarged in the drawing.

EXEMPLARY EMBODIMENT

[0018] A touch panel of an exemplary embodiment of the present inventionis described with reference to FIG. 1. A touch panel of this embodimenthas optically transparent upper substrate 1 that is made of polyethyleneterephthalate film, polycarbonate film, or the like, and has a thicknessranging from approximately 150 to 200 μm. On the bottom surface of theupper substrate, optically transparent upper conductive layer 2 made ofindium tin oxide, tin oxide, or other conductive materials, is formed byvacuum sputtering or other forming methods. On the other hand, on thetop surface of optically transparent lower substrate 3 made ofpolyethylene terephthalate resin, glass, acrylic resin, opticallytransparent lower conductive layer 4 is formed. On the top surface oflower conductive layer 4, a plurality of dot spacers 5 made of aninsulating resin, e.g. epoxy polymer and silicon polymer, are formed atpredetermined intervals. Dot spaces 5 serve to hold a predeterminedspace between upper conductive layer 2 and lower conductive layer 4.

[0019] Moreover, at both ends of upper conductive layer 2, a pair ofupper electrodes 6 is formed. On the other hand, at both ends of lowerconductive layer 4, a pair of lower electrodes 7 is formed. The pair ofupper electrodes 6 and the pair of lower electrode layers 7 arepositioned at orthogonal ends. However, in the description of FIG. 1, byrouting either upper electrode 6 or lower electrode 7, both electrodesare opposed to each other at the same end. Each of upper electrodes 6and lower electrodes 7 is formed by printing paste made of silver,carbon, or other conductive materials. These electrodes are covered withupper insulating layer 8 or lower insulating layer 9 made of polyesteror other materials.

[0020] Adhesive layer 15, an important element of the present invention,is a type of an adhesive layer of which bonding property is enhanced bypressing. Used in this embodiment is an adhesive material in which 1 to35 gram of a tackifier made of a thermoplastic oligomer is dispersed in100 gram of a thermoplastic resin, e.g. acrylic resin and polyesterresin.

[0021] Adhesive layer 15 is formed in a frame shape along the outerperiphery of upper insulating layer 8 or lower insulating layer 9 inthickness of 5 to 50 μm. Appropriately, an elastic modulus of theadhesive material made of a thermoplastic resin containing a tackifierdispersed therein is set to 10³ to 10⁸ Pa. The outer peripheries ofupper substrate 1 and lower substrate 3 are bonded by this adhesivelayer 15 so that upper conductive layer 2 and lower conductive layer areopposed to each other with a predetermined space held therebetween.Thus, the touch panel is configured.

[0022] Next, a method of manufacturing a thus structured touch panel isdescribed.

[0023] First, after an adhesive material including a solvent isscreen-printed on lower insulating layer 9 along the outer periphery oflower substrate 3, solvent is evaporated. Thus, frame-shaped adhesivelayer 15 approximately 1 to 1.5 mm wide is formed.

[0024] Then, upper substrate 1 is placed on lower substrate 3 so thatupper conductive layer 2 is opposed to lower conductive layer 4 with apredetermined space held therebetween. Adhesive layer 15 along the outerperipheries of upper substrate 1 and lower substrate 3 are pressed tobond upper substrate 1 and lower substrate 3 together. Thus, a touchpanel is completed.

[0025] Adhesive layer 15 made of a thermoplastic resin contains a.tackifier dispersed therein, and the tackifier increases flexibility ofthe adhesive layer. Thus, bonding is carried out with an adhesive areasubstantially increased by pressing. For this reason, adhesive layer 15as small as approximately 1 to 1.5 mm can provide a sufficient adhesivestrength.

[0026] Upper electrodes 6 and lower electrodes 7 of the produced touchpanel are connected to a detecting circuit (not shown) of electronicequipment. Depressing a position other than adhesive layer 15 on the topsurface of upper substrate 1, i.e. a touch sensitive area in whichdepressing operation and position-detecting operation are possible, witha finger, pen, or the like, flexes upper substrate 1 and brings upperconductive layer 2 in the depressed position into contact with lowerconductive layer 4. On the other hand, voltages are sequentially appliedto upper electrodes 6 and lower electrodes 7 by the detecting circuit.The detecting circuit detects the depressed position according toresistance ratios of these pairs of upper electrodes 6 and lowerelectrodes 7.

[0027] As described above, a touch panel of the present invention ismade of a thermoplastic resin containing tackifier dispersed therein.Also, upper substrate 1 and lower substrate 3 are bonded by adhesivelayer 15 of which bonding property is enhanced by pressing. Addition ofthe tackifier increases flexibility of adhesive layer 15 and performsbonding with an adhesive area substantially increased at pressing. Thus,the width of the adhesive layer can be as small as approximately 1 to1.5 mm. This can realize a smaller touch panel ensuring a predeterminedtouch sensitive area, and a method of manufacturing the touch panel.

[0028] Moreover, printing this adhesive layer 15 at least one of uppersubstrate 1 and lower substrate 3 eliminates a base of usual spacer 10to which the adhesive layers are applied on top and bottom surfacesthereof. This can reduce the number of constituent components and makethe touch panel less expensive.

[0029] Preferably, a thickness of adhesive layer 15 ranges from 5 to 50μm. This thickness ensures a sufficient space between the upper andlower conductive layers. With this thickness, the flexure stress createdon upper conductive layer 2 when the vicinity of adhesive layer 15 isdepressed is smaller than that caused by a thicker adhesive layer. Thus,breakage of upper conductive layer 2 can be prevented.

[0030] An elastic modulus of adhesive layer 15 can be adjusted accordingto the kind and polymerization degree of the thermoplastic resin and thekind and composition ratio of the tackifier added thereto. To attain theobject of the present invention, it is preferable that an elasticmodulus of adhesive layer 15 ranges from 10³ to 10⁸ Pa. Adhesive layer15 in the rage of the elastic modulus can prevent the followingproblems. Too soft adhesive layer 15 cannot provide a sufficientadhesive strength and upper substrate 1 and lower substrate 3 may peeloff easily. Too hard adhesive layer may make substrate 1 and lowersubstrate 3 difficult to adhere to each other.

[0031] Preferably, a thermoplastic resin for use in adhesive layer 15 isselected from at least one of acrylic resin and polyester resin. Acrylpolyol and polyester polyol have a larger number of reactive functionalgroups than other urethane polyol, and thus the crosslink densitythereof can be increased. For this reason, in addition to adhesivestrength at room temperature, holding strength at high temperatures canbe improved.

[0032] As a tackifier for use in adhesive layer 15, thermoplasticoligomers are preferable. Additionally, it is preferable to disperse 1to 35 gram of a thermoplastic oligomer in 100 gram of a thermoplasticresin. For example, terpene resin or the like is used as a thermoplasticoligomer. Terpene resin has excellent compatibility with thermoplasticresin, a main component. Moreover, heat resistance, weatheringresistance, and adhesion properties with respect to the adherend can beimproved.

[0033] Thermoplastic oligomers include modified terpene resin, terpenephenol resin and hydrogenated cyclic polymer in addition to the terpeneresin. Terpene resin complying with the isoprene rule is especiallypreferable.

[0034] In this embodiment, an adhesive composition in which 20 gram of aterpene resin is dispersed in 100 gram of an acrylic resin is used toproduce a touch panel. An elastic modulus of the adhesive compositionused measures 1×10⁵ Pa. Adhesive layer 15 in 1.0 mm wide and 30 μm thickis formed by printing the adhesive composition mixed in a solvent mainlycontaining butyl carbitol by screen-printing method on lower substrate9, and then by drying. Shelf test of the adhesion properties of theproduced touch panel in high temperatures and high humidity showed nofailure. On the other hand, shelf test of the conventional touch panelshown in FIG. 2 having 1.0-mm-wide spacer 10 under the same conditionscaused peeling in a part of the bonded position after the tests.

[0035] In another embodiment of the present invention, anisocyanate-containing curing agent is added to adhesive layer 15, and 1to 20 gram of this curing agent is dispersed in 100 gram of athermoplastic resin. For example, when the thermoplastic resin, a maincomponent, is a polyurethane resin, addition of theisocyanate-containing curing agent causes dehydration reaction, therebyforming urethane bonds having large cohesive energy. In other words, thecuring reaction cross-links resins, and an adhesive layer having a highcrosslink density is formed. For this reason, in addition to adhesivestrength at room temperature, holding strength at high temperatures isimproved. As a result, the width of adhesive layer 15 can be as small asapproximately 0.5 to 1.5 mm.

[0036] In the above description, acrylic resin or polyester resin isused as a thermoplastic resin in adhesive layer 15. However, the presentinvention can be implemented by using other resins, e.g. thermoplasticresin, such as epoxy resin modified by acrylic resin or polyester resin.

[0037] In the above description, only adhesive layer 15 without a baseis provided between the upper and lower substrates. However, adhesivelayers 15 can be applied to the top and bottom surfaces of a base madeof unwoven fabric, polyester film, or the like.

[0038] As described above, the present invention can provide a smallertouch panel ensuring a predetermined touch sensitive area, and a methodof manufacturing the touch panel.

What is claimed is:
 1. A touch panel comprising: an upper substratehaving an upper conductive layer formed on a bottom surface thereof; alower substrate having a lower conductive layer formed thereon, thelower conductive layer opposed to the upper conductive layer with apredetermined space held therebetween; and an adhesive layer bonding theupper substrate and the lower substrate; wherein the adhesive layer ismade of an adhesive material, and the adhesive material includes athermoplastic resin and a tackifier, and bonding property of theadhesive material is enhanced by pressing.
 2. The touch panel of claim1, wherein the adhesive layer is 1.0 to 1.5 mm wide.
 3. The touch panelof claim 1, wherein the adhesive layer is 5 to 50 μm thick.
 4. The touchpanel of claim 1, wherein the adhesive layer has an elastic modulusranging from 10³ to 10⁸ Pa.
 5. The touch panel of claim 1, wherein thethermoplastic resin is selected from at least one of acrylic resin andpolyester resin.
 6. The touch panel of claim 1, wherein the tackifier isa thermoplastic oligomer, and the adhesive material contains 1 to 35gram of the-tackifier in 100 gram of the thermoplastic resin.
 7. Thetouch panel of claim 1, wherein the adhesive material contain 1 to 20gram of an isocyanate-containing curing agent dispersed in 100 gram ofthe thermoplastic resin.
 8. The touch panel of claim 1, wherein theadhesive layer is 1.0 to 1.5 mm wide, and 5 to 50 μm thick; thethermoplastic resin contains at least one of acrylic resin and polyesterresin; the tackifier is a thermoplastic oligomer; the adhesive materialcontains 1 to 35 gram of the tackifier in 100 gram of the thermoplasticresin; and the adhesive layer has an elastic modulus ranging from 10³ to10⁸ Pa.
 9. A method of manufacturing a touch panel, the touch panelcomprising: an upper substrate having an upper conductive layer formedon a bottom surface thereof; a lower substrate having a lower conductivelayer formed thereon, the lower conductive layer opposed to the upperconductive layer with a predetermined space held therebetween; and anadhesive layer bonding the upper substrate and the lower substrate;wherein the adhesive layer is made of an adhesive material, and theadhesive material includes a thermoplastic resin and a tackifier, andbonding property of the adhesive material is enhanced by pressing; themethod comprising the steps of: printing the adhesive layer on at leastone of the upper substrate and the lower substrate; opposing the uppersubstrate to the lower substrate; and bonding the upper substrate andthe lower substrate by pressing the adhesive layer.
 10. The method ofmanufacturing a touch panel of claim 9, wherein the thermoplastic resincontains at least one of acrylic resin and polyester resin; thetackifier is a thermoplastic oligomer; and the adhesive materialcontains 1 to 35 gram of the tackifier in 100 gram of the thermoplasticresin.
 11. The method of manufacturing a touch panel of claim 10,wherein the adhesive material is made by dispersing 1 to 20 gram of anisocyanate-containing curing agent in 100 gram of the thermoplasticresin.